THE LACTOGENIC HORMONE 



internal secretion(s) of the ovaries. Inasmuch as normal 

 ovarian function requires the gonadotropic hormone(s) of the 

 pars glandularis, the latter indirectly controls the develop- 

 ment of the breasts. To what extent an internal secretion of 

 the pars glandularis, in the absence of the ovaries, can bring 

 about a development of the parenchyma of the breasts is a 

 matter of controversy. The clear-cut direct effect of extracts 

 of the pars glandularis — and with these, chiefly, this chapter 

 deals — is on the fully developed alveolar cells prepared to 

 secrete milk but unable to do so. Lactogenic extracts of the 

 pars glandularis seem to release the secreting mechanism so 

 that an abundant flow of milk follows the parenteral adminis- 

 tration of the hormone. In the normal lactating animal, how- 

 ever, there appear to be more complex interrelationships in- 

 volving the uterus, the ovary, and the lactogenic hormone^ 

 (and perhaps other hormones) of the pars glandularis. 



An interesting homologous effect of the lactogenic hormone 

 on the crop glands of the pigeon was discovered by Riddle and 

 Braucher (1931). Normally, the crop glands (two circum- 

 scribed portions of the dorsal part of the crop mucosa, 

 several square centimeters in area) undergo a marked de- 

 velopment during the last few days of the brooding period. 

 This occurs in both sexes. After hatching, the young are fed 

 for a short time by a mixture of food, and secretion and cells 

 of the crop mucosa — the "crop milk." In feeding the young, 

 either parent may regurgitate this mixture. At times other 

 than at the end of the brooding period (and also, of course, 

 before sexual maturity) the crop glands remain undeveloped. 

 Riddle and Braucher were able to show that marked develop- 

 ment of the crop glands could be produced by injecting ex- 

 tracts of the pars glandularis into pigeons about 75 days after 



^ There is evidence that extracts of the pars glandularis may produce lactogenic 

 effects unrelated to effects on growth, the gonads, and the thyroid. To designate the 

 lactogenic hormone, the names "galactin" (Turner) and "prolactin" (Riddle) have 

 been suggested. 



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